The use of organic polymers in numerous applications has grown in recent years to the degree that rigid polymers such as nylons and polyacetal resins have almost replaced the more conventional metal, wood, and ceramic materials. The development of low cost and efficient methods of preparing polyolefins has made them excellent candidates for a wider range of applications provided that certain physical properties such as heat distortion temperature, stiffness and hardness can be improved.
In recent years, much research has been conducted in the field to develop various methods for improving the physical properties of polyolefins. A vast majority of this research has been directed towards filling polyolefins with finely divided solids or fibrous fillers. One such method of providing filled polyolefins is by melt mixing the polyolefin with the filler material. This procedure, however, requires that the polyolefin be of relatively low molecular weight, that is, have an inherent viscosity less than about 1. While the resulting polymeric products produced by this method generally have increased stiffness, they do suffer from the disadvantage of lower elongation and increased brittleness.
Furthermore, serious problems of compounding these polymers prepared by melt mixing are encountered including the large power requirements for mixing machinery, degradation of the polymers by heating, nonuniformity of filler dispersion, and poor adhesion of the polymer to the filler, even when coupling agents are employed.
Recently, various methods have been proposed and developed to decrease the problems mentioned above, the most widely used method being the polymerization of an olefin in the presence of selected fillers. One suggested method of effecting olefin polymerization on the filler is by employing a coordination catalyst. In this method, well-known coordination catalysts comprising the combination of transition metal halides and esters and a reducing compound such as an organometallic compound of a metal of Group Ia, IIa or IIIa of the Periodic Table of Elements are generally employed. This method in general, however, has not provided toughness in highly filled polyolefin composition.
Another method of improving the physical properties of polyolefins using a filler material is disclosed in U.S. Pat. No. 3,950,303 to Lipscomb. This reference describes a process for polymerizing olefins onto a chromium-modified filler in the presence of an organometallic compound. Moreover, the process disclosed by Lipscomb involves (a) contacting an inorganic filler material with a solution of a chromium(III) compound whereby the chromium compound is adsorbed onto the surface of the filler; (b) activating the chromium-modified filler by drying; (c) dispersing the filler as a slurry in an inert, liquid hydrocarbon; (d) adding an organoaluminum compound to said slurry; and (e) polymerizing an olefin in said slurry. This method is said to result in the formation of an essentially homogeneous, filled polyolefin composition having a good combination of hardness, toughness and stiffness.
U.S. Pat. No. 4,104,243 to Howard, Jr. relates to a process for preparing low viscosity inorganic filler compound dispersions and the use of the same in the preparation of polyolefin/inorganic filler compositions. More specifically, the process as described in the reference involves dispersing a large amount of a finely divided inorganic filler compound as a slurry in an inert hydrocarbon diluent in the presence of an organoaluminum compound. This dispersion may then by contacted with a transition metal polymerization catalyst and an olefin to produce a polyolefin/filler composition.
U.S. Pat. No. 4,473,672 to Bottrill relates to a process of producing a polymer composition which is a composite material containing an olefin polymer and a filler. Moreover, the patentee discloses a polymer composite which is produced by polymerizing an olefin monomer in the presence of a catalyst system obtained by reacting a filler material with (a) an organic magnesium compound which contains a halogen or (b) an organomagnesium compound and thereafter with a halogen-containing compound; and then treating that reaction product with a transition metal compound, which is preferably TiCl.sub.4, and an organic activating compound. The resultant homogeneous composites are said to have good flow characteristics.
This method disclosed by Bottrill, however, suffers from the disadvantage that the composite will contain a halogen, therefore, it is necessary to carry out a deashing step. The use of a deashing step is undesirable since those skilled in the art are aware that halogens can adversely affect the polymer product as well as cause corrosion of the machinery used to process the final product.
One such method of overcoming the deashing problem described above is disclosed in U.S. Pat. No. 4,564,647 to Hayashi et al. which relates to a process for producing a polyethylene composition which comprises polymerizing ethylene in the presence of a catalyst comprising a contact treatment product of a high activity catalyst component, a filler and an organoaluminum compound. This process has no need for a deashing step since the catalyst employed has a remarkably high activity even though the catalyst contains very low amounts of a halogen.
Schoppel et al., Makromal. Chem., Rapid Commun. Vol 3, (1982), pp. 483-488 provides a procedure which leads to filled polymers with strong polymer-filler interactions by fixing one component of the catalyst onto the surface of the filler. The reference typically uses TiCl.sub.4 as a fixing agent and the catalysts are normal Ziegler catalysts such as Mg(OEt).sub.2 /TiCl.sub.4 /Al(iBu).sub.3. The procedure described by Schoppel et al. is said to result in high catalyst activity compared with prior art systems.
Despite the current state of the art, none of the references disclosed hereinabove relate to the current method of in-situ filling of polyolefins. That is, none of the references disclosed hereinabove relate to a method to reactor-fill polyolefin comprising the steps of (a) adding a sufficient amount of at least one alpha-olefin to a filler such that a sticky prepolymer can be formed in-situ; (b) prepolymerizing the reaction mixture of step (a) by contacting said mixture in no specific order with a high activity catalyst, a cocatalyst and, if necessary, a cocatalyst modifier wherein said contacting step causes the formation of a sticky prepolymer on the surface and in the pores of the filler; and (c) adding an alpha-olefin under olefin polymerization reaction conditions to the reaction product of step (b) to form a reactor-filled composite having a high filler content and high melt flow. The addition of the alpha-olefin to the filler causes the filler particles to blend in-situ with the matrix polymer and results in a fewer number of fines in the composite product.